Pd-1 Pathway Upregulation By Orchiectomy Attenuates The Aldosterone And High Salt Induced Aortic Aneurysms In Male Mice

Objective: Male sex is a well-established risk factor for abdominal aortic aneurysms (AAA) but the underlying mechanisms remain to be fully understood. Using an aldosterone and high salt (Aldo/salt) induced AAA mouse model, we have demonstrated that androgen and its receptor mediate the high susceptibility to Aldo/salt induced AAA. The current study further investigates the mechanisms downstream of androgen. Approaches and Results: - To dissect the mechanisms connecting androgen and AAA, aortas were collected for RNA sequencing from 3 groups of 10-month-old wild-type mice #1 intact mice; #2 orchiectomized mice; and #3 orchiectomized mice plus DHT. All mice were given Aldo/salt for 7 days. Differentially expressed genes were analyzed using DESeq2 in R. We filtered genes that were upregulated in group #2 compared to group #1 and the up-regulation was reversed in group #3 by the DHT, or vice versa (fold change >1.5 and padj <0.05). Selected genes were run for gene ontology analysis in Enrichr (database Bioplanet 2019). Many pathways related to T cell activity were significantly enriched, particularly PD-1 signaling was one of the top pathways upregulated in orchiectomy group #2. PD-1 is known for its role as an immune checkpoint, and inflammation is a major hallmark for AAA development. Therefore to explore the role of PD-1, we first confirmed the PD-1 mRNA changes in aorta by qPCR. Secondly, IHC staining also showed PD-1 protein was significantly increased in the spleen of orchiectomized mice compared to intact controls. Finally, to investigate the potential causal role of PD-1 in the androgen-mediated aortic aneurysms formation, we injected αPD-1 antibody or control IgG antibody to orchiectomized mice 3 days before and during the 8 weeks of Aldo/salt administration. Results showed that 5 out of 12 αPD-1 mice, while none of the 8 control mice developed aortic aneurysms (p<0.05). Conclusions: PD-1 pathway is involved in the androgen associated high susceptibility of Aldo/salt induced aortic aneurysms in mice.